The present invention relates to a process for producing carbonyl difluoride (COF2), which is useful as a reagent in organic syntheses and as cleaning gas and etching gas for semiconductor producing apparatuses.
The synthesis of COF2 can be classified into (a) a first process in which carbonyl dichloride (phosgene) is reacted with a suitable fluorination agent (e.g., hydrogen fluoride, antimony trifluoride, arsenic trifluoride, and sodium fluoride), thereby conducting a halogen exchange between chlorine atom and fluorine atom, and (b) a second process in which carbon monoxide is reacted with a suitable fluorination agent (e.g., fluorine and silver difluoride). Japanese Patent Unexamined Publication JP-A-54-158396, corresponding to U.S. Pat. No. 4,260,561, discloses a process for producing carbonyl difluoride by reacting phosgene with hydrogen fluoride in the presence of acetonitrile.
The first process has a problem of using phosgene, which is a highly toxic substance. Furthermore, the COF2 synthesized by the first process may contain impurities of (a) carbonyl fluorochloride derived from chlorine and (b) carbon dioxide derived from water, for example, of the fluorination agent. It is difficult to remove these impurities from the COF2.
The second process can be conducted by reacting carbon monoxide with fluorine. This reaction may, however, occur explosively. Furthermore, the obtained carbonyl difluoride may be low in purity due to its containment of carbon tetrafluoride and other impurities caused by heat of the reaction.
It is possible to relatively safely synthesize COF2 with high purity by reacting carbon monoxide with silver difluoride. With this reaction, however, yield may be in a range of 70-85%, and the resulting carbonyl difluoride may contain carbon dioxide as an impurity, as described in Inorg. Synth., 6, 155 (1960). Furthermore, silver difluoride is extremely high in reactivity. Therefore, it decomposes by a reaction, for example, with water in the air and thereby turns into silver monofluoride. Thus, a substantial amount of silver difluoride turns into silver monofluoride by putting silver difluoride into a reactor in the air, thereby lowering yield. Furthermore, silver difluoride is high in water absorbent property. Thus, silver difluoride tends to absorb water upon putting silver difluoride into a reactor in the air. This absorbed water tends to cause hydrolysis of carbonyl difluoride to form carbon dioxide and hydrogen fluoride, thereby lowering the target compound (carbonyl difluoride) in purity and yield.
J. Amer. Chem. Soc., 102, 7572-7574 (1980) discloses a reaction of fluoroethane with ozone to produce carbonyl fluoride. J. Amer. Chem. Soc., 62, 3477 (1940) discloses a process for producing carbonyl fluoride using an equilibrium reaction between carbon monoxide and carbon tetrafluoride. These two reactions may be low in yield and purity and therefore may not be suitable for industrial processes for producing carbonyl difluoride.